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A brief discussion on the difference between Arrays.asList() and ArrayList types

高洛峰
Release: 2017-02-04 10:06:12
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<pre name="code" class="html">Arrays.asList()<br></p>
<p>Convert an array Converted into a List object, this method will return an ArrayList type object. This ArrayList class is not the java.util.ArrayList class, but a static internal class of the Arrays class! If you use this object to add, delete, and update the list, an UnsupportedOperationException will be reported. </p><div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:java;toolbar:false"><pre name="code" class="html">自己测试:<span>   </span>//arrayList
<span>        </span>List list = new ArrayList();
<span>        </span>list.add("yz_b_insert");
<span>        </span>list.add("yz_b_del");
<span>        </span>list.add("yz_b_update");
<span>        </span>list.add("yz_b_see");
<span>        </span>System.out.println(list.contains("yz_b_update")+"=="+list);
<span>        </span>//arrays.asList()
<span>        </span>String dd = "yz_b_insert,yz_b_del,yz_b_update,yz_b_see";
<span>        </span>List list2 = Arrays.asList(dd);
<span>        </span>System.out.println(list2.contains("yz_b_update")+"@@@@@"+list2);
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Output result:

<pre name="code" class="html">arraylist:true==[yz_b_insert, yz_b_del, yz_b_update, yz_b_see]
<pre name="code" class="html">arrays.asList():false@@@@@[yz_b_insert,yz_b_del,yz_b_update,yz_b_see]
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##If you use
contains to determine the existence of a certain string in the collection. Note that the <pre name="code" class="html">arraylist conversion is not available <p></p>I cannot test it , there are experts who can give some advice <p></p>The following are the resources found online <p><div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:java;toolbar:false"><span style="color: rgb(102, 102, 102); font-family: Tahoma;">为什么Arrays.asList产生的List是不可添加或者删除,否则会产生UnsupportedOperationException,就可以得到解释了。 </span><br style="color: rgb(102, 102, 102); font-family: Tahoma;" /><br style="color: rgb(102, 102, 102); font-family: Tahoma;" /><span style="color: rgb(102, 102, 102); font-family: Tahoma;">如果我们想把一个变长或者数据转变成List, 而且期望这个List能够进行add或者remove操作,那该怎么做呢? </span><br style="color: rgb(102, 102, 102); font-family: Tahoma;" /><br style="color: rgb(102, 102, 102); font-family: Tahoma;" /><span style="color: rgb(102, 102, 102); font-family: Tahoma;">我们可以写一个类似的方法,里面直接采用java.util.ArrayList即可。 </span><br style="color: rgb(102, 102, 102); font-family: Tahoma;" /><br style="color: rgb(102, 102, 102); font-family: Tahoma;" /><span style="color: rgb(102, 102, 102); font-family: Tahoma;">比如: </span><br style="color: rgb(102, 102, 102); font-family: Tahoma;" /><pre class="java" name="code" style="color: rgb(102, 102, 102); background-color: rgb(255, 255, 255);">import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class MyArrays {
    public static <T> List<T> asList(T... a) {
        List<T> list = new ArrayList<T>();
        Collections.addAll(list, a);
        return list;
    }
}
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The test code is as follows:

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class Test {
    @SuppressWarnings("unchecked")
    public static void main(String[] args) {
        List<String> stooges = Arrays.asList("Larry", "Moe", "Curly");
        print(stooges);
        List<List<String>> seasonsList = Arrays.asList(retrieveSeasonsList());
        print(seasonsList);
        /*
         * 自己实现一个asList方法,能够添加和删除。
         */
        List<String> list = MyArrays.asList("Larry", "Moe", "Curly");
        list.add("Hello");
        print(list);
    }
    private static <T> void print(List<T> list) {
        System.out.println(list);
    }
    private static List<String> retrieveSeasonsList() {
        List<String> seasonsList = new ArrayList<String>();
        seasonsList.add("Spring");
        seasonsList.add("Summer");
        seasonsList.add("Autumn");
        seasonsList.add("Winter");
        return seasonsList;
    }
}
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Output result:

[Larry, Moe, Curly]

[[Spring, Summer, Autumn, Winter]]
[Larry, Moe, Curly , Hello]

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